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Water Demand Management (WDM)
Lecture 5Lecture 5
IWRM � IWRM, Global Water Partnership 2000
� A process which promotes the coordinated development and management of water, land, and related resources in order to maximize the economic and social welfare in an equitable manner without compromising the sustainability
� Four Dimensions:
1. Resources1. Resources
� Quantity
� Quality
2. Water users
3. Spatial Scale
� Jurisdiction level
� System boundaries
4. Temporal Scales and patterns
Water Demand Management (WDM)� Water Demand management aims at achieving desirable demands
and desirable uses. It influences demand in order to use a scarce resource efficiently and sustainably.
� WDM is not necessarily the same as decreasing water demand; in certain situations managing the demand may mean to stimulate the demand that had been suppressed, here we have to improve water services and increase water consumption
� WDM uses technical, legal and economic incentives in combination with awareness raising and education; in order to achieve more desirable consumption patterns, both in terms of distribution between sectors and quantities consumed, coupled with an increased reliability of supply.
� WDM is always concerned with increasing the efficient use of water. Minimizing leakages is often the most cost-effective strategy towards system's improvement.
Water Demand Management
� Goals of demand-side management of water
� Increased efficiency of water use
� Safeguard the right of access to water for future generations
� Improve allocation among competing users� Improve allocation among competing users
� Decreased need for large investments in infrastructure (like dams, Desalination Plants)
� More cost effective water use
� Changes to the nature of water demand and the way people use water
WDM Tools / Instruments� Technical / regulatory tools
� Reduction of water losses� Leak detection and repair� Inspection of illegal connections� Modern irrigation techniques� More crop for drop
� Improved O&M� Metering� Rationing� Rationing� Cropping patterns� Timing and regulations of outdoor irrigation� Dual distribution system
� Good quality for drinking and cooking� Lower quality for other uses� Internal recycling
� Water savings appliances/devices� Automatic taps� Spray showers� Dual flush system
� Rainwater harvesting / promote reclaimed WW (supply side)
WDM Tools / Instruments
� Social tools� Behavioral changes� Public awareness� Education curricula
� Economic tools� Water pricing
� Increasing block tariff� Increasing block tariff� Implementation incentives
� Subsidies� Taxes� Loans� Promotions for compliance � Fines / penalties / fees
� Legal tools� Policies / laws � Regulatory framework
Global Water Resources
Global Water Resources
River Basin Water Balance
( ) QAETPt
S−−=
∆
∆
Water Demand – Municipal &Industrial (M&I)
� Factors:
� Population and population density
� Housing type and standard of living
� Sanitation type
� Climate conditions� Climate conditions
� Economic conditions and income level
� Water availability – Rationing
� Water quality
� Pricing policies and tariff structure
Per - Capita Demand
� Basic Human Needs
� WHO (guidelines for small communities)
� Average 150 l/c/d
� Minimum 100 l/c/d
Per - Capita Demand
150 l/c/d300 l/c/d420 l/c/d165 l/c/d
Per - Capita Demand
ا�حتياجات الفردية1)ا�ستعمال داخل المنزل ( المنزلي �
لتر للفرد في اليوم 100=الحد ا�دنى �
لتر للفرد في اليوم 150= المتوسط �
)يشمل متطلبات المساحات الخضراء و الدفاع المدني ( الخدمات العامة �
من ا�جمالي %5تقدر بحوالي �
الصناعي � 2020 في %14حاليا الى %7من
1- WHO guidelines for water supply systems in small communities
2020 في %14حاليا الى %7من �
من مصادر مياه الشرب تعتبر مطابقة للمواصفات المحلية% 15أقل من *
ا*حتياجات ا*جمالية
*
* Based on PCBS including the returnees before 2000* Based on PCBS including the returnees before 2000
Population
� Growth rate:
� dP/dt = change in population during time step (capita)
� B = number of birth per unit of time (capita/year):
P
OIDBdt
dp−+−=
Similar to Water Balance
b is the birth rate which the amount of
� D = number of death per unit of time (capita/year)
� I = immigration (capita/year)
� O = emigration (capita/year)
� L= life expectancy (year)
L
PdD =
L
PbB =
b is the birth rate which the amount of
children born per person during his/her life
d is the death rate
d = 1 : steady state situation
d < 1 : population is growing where more
young people than old people.
d > 1 : more elder people than young
people ( case of china b=0.5) where b < 1.
Population
( )PrP
L
db
dt
dp.=
−=
trePP
..=
Ignoring immigration and emigration
1- if (b-d)> 0: more children are born than die
2- b=d: the population is constant.
.ConstP =∆
trePP
.
0.=
The exponential growth model can also be written as:
Other models: Linear Model:
trPP )1(0 +=
Population
trePP
.
0.=
Example:
Number of children 4 2000
2500
3000
po
pu
lati
on
r=0.033 r=0.05
r=(4-2)/60=0.033
Number of children 5
r=(5-2)/60=0.05
0
500
1000
1500
1 3 5 7 9 11 13 15 17 19
po
pu
lati
on
years
Population
� Other models: Saturation model
Ps
P
t
Gaza Population
15
97
00
0
18
51
00
0
21
46
00
0
1,300,000
1,400,000
1,500,000
1,600,000
1,700,000
1,800,000
1,900,000
2,000,000
2,100,000
2,200,000
2,300,000
PO
PU
LA
TIO
N
WSSPS estimation
(50,000 returnees,
decreasing population
growth rate from 3.5%
to 3.1% )
13
77
50
0
15
97
00
0
10
22
20
7
0
100,000
200,000
300,000
400,000
500,000
600,000
700,000
800,000
900,000
1,000,000
1,100,000
1,200,000
1,300,000
19
68
19
70
19
72
19
74
19
76
19
78
19
80
19
82
19
84
19
86
19
88
19
90
19
92
19
94
19
96
19
98
20
00
20
02
20
04
20
06
20
08
20
10
20
12
20
14
20
16
20
18
20
20
YEAR
PO
PU
LA
TIO
N
ACTUAL POPULATION
(ISRAELI DATA)
ACTUAL POPULATION
(PALESTINIAN DATA) 11
10
00
0
Population Pyramid
Irrigation Water Demand
ETo: Reference evapotranspiration: The evapotranspiration rate from a reference surface, not short of water. The reference surface is a hypothetical grass reference crop with specific characteristics
Single Crop Coefficient - Kc
Case A: Pan placed in short green cropped area Case B: Pan placed in dry fallow area
RH mean(%)
low < 40
Medium 40 - 70
High> 70
low < 40
medium 40 - 70
high > 70
Wind speed (m s-1)
Windward sidedistance of
Green crop (m)
Windward side distance of dry
fallow (m)
Light 1 .55 .65 .75 1 .7 .8 .85
< 2 10 .65 .75 .85 10 .6 .7 .8
100 .7 .8 .85 100 .55 .65 .75
1000 .75 .85 .85 1000 .5 .6 .7
Moderate 1 .5 .6 .65 1 .65 .75. .8
2-5 10 .6 .7 .75 10 .55 .65 .7
100 .65 .75 .8 100 .5 .6 .65
1000 .7 .8 .8 1000 .45 .55 .6.
Strong 1 .45 .5 .6 1 .6 .65 .7
5-8 10 .55 .6 .65 10 .5 .55 .65
100 .6 .65 .7 100 .45 .5 .6
1000 .65 .7 .75 1000 .4 .45 .55
Very strong 1 .4 .45 .5 1 .5 .6 .65
> 8 10 .45 .55 .6 10 .45 .5 .55
100 .5 .6 .65 100 .4 .45 .5
1000 .55 .6 .65 1000 .35 .4 .45
Factors Influencing Kc� Crop height: The crop height influences the aerodynamic resistance
term (ra) of the FAO Penman-Monteith equation and the turbulent transfer of vapour from the crop into the atmosphere.
� Albedo (reflectance) of the crop-soil surface. The albedo is affected by the fraction of ground covered by vegetation and by the soil surface wetness. The albedo of the crop-soil surface influences the net radiation of the surface, Rn ,which is the primary source of the energy exchange for the evaporation process
� Canopy resistance: The resistance of crop to vapour transfer is affected by leaf area (number of stomata), leaf age and condition, and the degree of stomatal control. The canopy resistance influences the surface resistance, rs
� Evaporation from soil, especially exposed soil.
Initial stage Crop development stage Mid-season stage Late season stage
Estimation of ET0
ET reference evapotranspiration [mm day-1],
Penman-Monteith Method
http://www.fao.org/docrep/X0490E/x0490e01.htm
� ETo reference evapotranspiration [mm day-1],
� Rn net radiation at the crop surface [MJ m-2 day-1],
� G soil heat flux density [MJ m-2 day-1],
� T mean daily air temperature at 2 m height [°C],
� u2 wind speed at 2 m height [m s-1],
� es saturation vapour pressure [kPa],
� ea actual vapour pressure [kPa],
� es - ea saturation vapour pressure deficit [kPa],
� D slope vapour pressure curve [kPa °C-1],
� γ psychrometric constant [kPa °C-1].
Tedious Calculations
G ???
Rn ???
Epan Method
� ETo reference evapotranspiration [mm/day]
� Kp pan coefficient [-]
� Epan pan evaporation [mm/day].
ETo = Kp Epan
Effective Rainfall (USDAS-SCS Method)
( ) ( )0000955.0834.0 1093.225.1ET
PfPeff ∗−∗=
f = correction factor depends on average net application depth or soil moisture depletion before each irrigationor soil moisture depletion before each irrigation
P = the gross monthly rainfall in mmET0 = the monthly reference evapotranspiration
effPKcETCWR −∗= 0
Gaza Example
Gaza Example
Gaza Example
Crop Category Crop Type
Citrus Orange / lemon / grapefruit
Fruit trees Apples / pears / peaches / apricots / almonds
Vegetables1 Cucumber / squash / cabbage
Vegetables2 Tomato / sweet peppers / egg plants / potato
Field crops Wheat / barleyField crops Wheat / barley
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Citrus 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.65 0.65 0.65 0.65 0.65
Fruit trees 0.9 0.9 0.9 0.65 0.65 0.65 0.65 0.4 0.4 0.4 0.4 0.9
Vegetables1 1.15 1.15 0.95 0.6 1 1 0.75
Vegetables2 0.8 0.6 0.6 1.15 1.15 0.8 0.6 1.15 1.15 0.8
Field crops 1.15 0.4 0.3 0.3 1.15
Gaza Example
Gaza Example
Gaza Example
Gaza Example
Gaza Example
Demand-Resources Gap
Other Water Demands� Environmental Demand
� Environmental flow: the quantity and quality of water required to sustain aquatic ecosystems and the ecological components, processes and functions on which people depend
� Ecological functions of flow� Extreme low (drought) flows
� Population regulation; life history cues� Population regulation; life history cues
� Low (base) flows� Provide habitat for aquatic biota, maintain water temperature and
water chemistry, provide drinking water for terrestrial animals
� High flows� Shape river channel, prevent encroachment of riparian vegetation,
flush sediments and pollutants, maintain estuaries and floodplain
� Hydropower� Power generation requirements
E = P T = et eg ρ g Q H T
Water PricingDublin and Rio conferences, Agenda 21: Water should bemanaged as an economic good, provided water for drinkingpurposes and other basic needs are made available at prices thatare widely affordable locally
Water Pricing make a key instrument for the implementation of Demand Management:
� Increased price reduces the demand;
� Increased price increases supply (firstly, becausemarginal projects may become affordable andsecondly because it becomes attractive to reducelosses);losses);
� increased prices facilitate reallocation amongsectors;
� Increased prices improve managerial efficiency.
Cost of Water
� Water pricing should have two purposes:� to recover costs� to enhance water use efficiency
� External costs (economic externalities): environmental damage,pollution, effect on downstream users and health hazards
� The economic price should also reflect the scarcity of theresource, which is generally expressed in the opportunity cost (thecost of not being able to use the resource for another social oreconomic activity).
The following questions to be answered:
� How should we determine the full social cost
with respect to long-term marginal social
costs and external environmental cost?
� How should we identify users (consumptive� How should we identify users (consumptive
users, non-consumptive users and polluters)
to which costs should be charged?
Goodman (1984) stated that :
� The economic value of a product or service
from a water resources is estimated as the
amount of users are willing to pay for it.
� This is not entirely true since water is
essential to life and there is no alternative foressential to life and there is no alternative for
it .
� The variation of the willingness to pay can be
conceptually shown by the curve of price per
demand.
Price vs. Demand
where
� Q is the quantity of demand for the good
EcPQ = Q
demand for the good
� P is the price of the good
� c is a constant
� E is the elasticity of demand (-1 , 0) (the slope of the curve)� Price
� Type of use PAssumptions:• constant incomes • constant preferences (willingness to pay or economic value of the water)
Price vs. Demand
150
200
250
300
Q (
l/c
/d)
Elastic
Rigid
0
50
100
150
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Price ($/m3)
Q (
l/c
/d)
Price vs. Demand
250
300
350
400
450
Q (
l/c
/d)
low income
high income
0
50
100
150
200
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Price ($/m3)
Q (
l/c
/d)
Elasticity of Demand
� If E ≤-1, the response to a price increase is said to be elastic or reactive.
� If -1<E, the response to a � If -1<E, the response to a price increase is said to be inelastic or rigid.
� Essential needs� More rigid� No alternatives
� industry and agriculture � More elastic� Alternatives available
Elasticity of Demand� Example (1):
� What is E if the a price increase by 100% (P1=2*P0) resulted in a 20% decrease in water use (Q1=0.8Q0)?
� dP/P = (P1-P0)/P0 = (2P0-P0)/P0 = 1 � dQ/Q = (Q1-Q0)/Q0 = (0.8Q0 -Q0)/Q0 = -0.20 � E = -0.20/1= -0.20 (rigid)� E = -0.20/1= -0.20 (rigid)
� Example (2): � What is E if the price is increased by 10% and a decrease of the
consumption of 5%?
� dP/P = 0.1� dQ/Q = -0.05� E = -0.05/0.1= -0.50 (rigid)
Elasticity of Demand
� Concluding: � the elasticity of water consumption is generally
low. � the price elasticity is greater when the price is
higher. higher. � in the household sector, the price elasticity varies
between -0.15 and -0.70. � with respect to drinking water the demand-price
relation will never be elastic (E < -1) � in the industrial sector, the majority of estimates
are in the range of -0.45 to -1.37.
� Example:
Does increasing price result in increasing revenues?
� Revenues or the amount of money people are willing to pay = QP
� If we compute the relative change in the revenue :
� (1+E)>0 , an increase of the price results in an increase of a revenue
Elasticity, water use and climate types
rigid
EThe availability of
alternative of
water
elastic
Go to 8-SMetaxas.pdf file
Increasing Block Tariff� Considerations
� Cost recovery
� Equity (access to basic needs)
� Block purpose:
Cross-subsidy � Cross-subsidy from rich to poor users
� Compromise between full cost recovery and equity
Increasing Block Tariff ExampleBlock 1:
� the poorest households have access to a lifeline amount of water and do not spend more than a certain percentage of their income on water
� subsidized
Block2:� ideal’ per capita water consumption level
� ensure “well-being” e.g. twice the lifeline amount
� charged at the full cost of water supply for the amount above block1� charged at the full cost of water supply for the amount above block1
� some subsidy
Block 3:� above the well-being amount but less than a certain upper limit (e.g. 4 times
the lifeline amount)
� Charged at full cost of water over their entire use
Block 4:� water use above the amount specified in the third block will be charged at a
rate that will off-set the subsidy received by households falling within blocks 1 and 2
Increasing Block Tariff Example
Increasing Block Tariff South Africa Example
